1. Field of the Invention
The present invention relates to techniques for miniaturizing active matrix displays and for enhancing their reliability.
2. Description of the Related Art
The state of a panel forming the prior art active matrix display is shown in FIG. 4 in cross section. As can be seen from this figure, a sealing material 402 surrounds a pixel region 404 and so only the pixel region 404 of the active matrix display is in contact with a liquid crystal material. TFTs in a peripheral driver circuit region 403 are in contact with the atmosphere. These are remains of the prior art techniques in which only pixel TFTs are present on the substrate of an active matrix display, and in which a driver circuit is an externally attached IC. In these prior art techniques, the position at which the driver circuit is mounted is not optimized where the pixel region 404 and the peripheral driver circuit region 403 are formed on the same glass substrate 401.
In the prior art active matrix display, the TFTs of the driver circuit are exposed. Therefore, during assembly of the panel, the substrate of the active matrix display must be handled with meticulous care. Under these circumstances, there is a demand for an active matrix display which assumes such a form that the display is handled with ease during fabrication processes. Pixels are protected by the liquid crystal material, the sealing material, and other materials for securing high reliability. On the other hand, the driver circuit is coated with only a thin oxide film. Therefore, the driver circuit does not have sufficient temperature resistance, and is vulnerable to contamination.
In order to minimize the damage sustained during assembly of the panel of the driver circuit of an active matrix display in an attempt to solve the problems with the reliability, the driver circuit of the active matrix display may take such a form that the user cannot directly touch it. Accordingly, as shown in FIG. 1, the peripheral driver circuit region 103 of the aforementioned active matrix display is buried either in the liquid crystal material or in the sealing material.
One invention disclosed herein is an active matrix display which is similar to the above-described active matrix display where pixel TFTs and TFTs forming the driver circuit for the pixels are formed on the same substrate. A liquid crystal material is sealed in so that both pixel TFTs and TFTs of the driver circuit are in contact with the liquid crystal material directly or via a thin film.
Generally, a thin-film transistor (TFT) is coated with an interlayer dielectric film consisting of a film of silicon oxide or the like. Therefore, the TFT is in contact with the liquid crystal material via this dielectric film. By adopting this structure, the TFTs of the peripheral driver circuit can be substantially sealed in the liquid crystal material. That is, the TFTs of the peripheral driver circuit can be sealed by the liquid crystal material.
Another invention has a pair of transparent substrates between which a liquid crystal material is held. TFTs are arranged in rows and columns on the surface of one of the substrates, thus forming a matrix circuit. A peripheral driver circuit consisting of TFTs is connected with the matrix circuit. A liquid crystal material or sealing material is present on the top surface of the peripheral driver circuit. A space for accommodating an integrated circuit connected with the peripheral driver circuit is formed between the substrates.
A specific example of the above-described structure is shown in FIG. 2 which is a schematic cross section of an active matrix display having a pair of glass substrates 202 and a liquid crystal material 209 held between the substrates. The configuration shown in FIG. 2 has TFTs 207 of the active matrix circuit; TFTs 208 of the peripheral driver circuit for driving the TFTs 207, and an integrated circuit 211 for sending video signals and various control signals to the TFTs 208 of the peripheral driver circuit.
In the structure shown in FIG. 2, the liquid crystal material exists on the top surface of each TFT 208 of the peripheral driver circuit. The integrated circuit 211 sealed by a sealing material 210 is disposed in a space formed between the glass substrates 202.
Another invention is an active matrix display characterized in that the pixel TFTs of the active matrix display and the TFTs of the driver circuit for activating the pixels are present on the same substrate, and that the TFTs of the driver circuit are sealed by the sealing material.
A specific example of the above-described structure is shown in FIG. 3, where TFTs 308 forming the peripheral driver circuit are sealed by a sealing material 310.
The peripheral driver circuit region is located either within the region where the liquid crystal material exists or within the sealing material. It substantially follows that the peripheral driver circuit region is sealed in the liquid crystal material or in the sealing material. This can prevent extraneous moisture from encroaching on the peripheral driver circuit region of high packaging density. Furthermore, the effects of stress can be mitigated.
To minimize the damage of a drive circuit in an active matrix liquid crystal display device in a panel assembly process, and to solve the problem of reliability, an active matrix liquid crystal display device is required to be manufactured such that the drive circuit thereof cannot be touched directly. Therefore, a peripheral drive circuit region 803 of an active matrix liquid crystal display device is mounted in liquid crystal or sealing material as shown in FIG. 8.
FIG. 8 shows an embodiment in which a single glass substrate 801 is constituted of four panels. The substrate shown in FIG. 8 is constituted of a peripheral drive circuit 803 and a pixel area 804 which are integrated on the same glass substrate. The pixel area 804 is constituted of at least one thin-film transistor which is connected to a pixel electrode arranged like a matrix.
In FIG. 8, only the glass substrate 801 on which each circuit is formed is shown, however, another glass substrate opposite to it is actually arranged. A counter electrode is arranged on the opposite glass substrate not shown.
Further, in the constitution shown in FIG. 8, the active matrix liquid display device is divided by sealing material 802 so as to realize a manufacturing of a plurality of active matrix liquid crystal display panels on a pair of glass substrates. With such a constitution, the productivity and the reliability can be simultaneously enhanced.
It should be noted that although the width of the sealing material 802 is equal in FIG. 8, it may be widened to provide a margin for cutting the glass substrate 802 in an area where it is cut. For example, as shown in FIG. 9, the width of the cross area of a sealing material 800 that divides liquid crystal display device may be approximately twice as wide as that of an edge area around the glass substrate 801. In FIG. 9, the same reference numeral as in FIG. 8 denotes the same member.